1. Field of the Invention
This invention relates to automatically-actuated safety valves used in gas mains. More precisely, the invention relates to a safety device inserted into a fluid pipeline of a set minimal sectional area to protect it against excessive flow rates of fluid circulating in it from upstream to downstream. The device comprises a tube with open upstream and downstream ends and a central circulatory passage for the fluid, retention means to hold the tube in place within the pipeline, and means of regulating the fluid circulation including a central valve. The device changes between a rest configuration, which it adopts in the event of a normal fluid flow rate and in which the central valve frees the central circulatory passage, and a safety configuration, which it adopts in the event of an excessive fluid flow rate and in which the central valve obstructs the central circulatory passage. The central valve itself includes a valve seat embedded in the tube, a central valve closure member selectively applied to the valve seat, and a spring exerting an elastic opening force on the central valve closure member. This force solicits the central valve closure member at a distance from the valve seat, counter to a closure force exerted on this central valve closure member by loss of head which increases with the flow rate of the fluid in the pipeline.
2. The Prior Art
Devices meeting this definition by extension are known in the prior art, as demonstrated, for example, in U.S. Pat. No. 2,926,690 and U.S. Pat. No. 5,293,898. Some fluid pipelines require special safety measures, imposed by the nature of the fluid to he transported and by any possible risk of damage to the pipes which constitute these pipelines.
For example, the gas mains in urban areas generally lie under roads and pavements, that being under public land structures likely to undergo various works, notably earthworks. And, if a gas pipe is accidentally pulled up or severed during such works, the immediately resulting gas leak creates a very high risk of fire or explosion. In this context, safety valves have been developed to obstruct the gas pipes as soon as an abnormally high gas flow rate is detected.
The current security valves can only be mounted onto new pipelines being laid, or possibly to extant pipelines, but only when they are being renovated. Indeed, as extant pipelines may have been laid at different periods and according to different standards, meaning that they do not necessarily have very precisely defined diameters, and have obstacles, flashes, buckles restrictions, and/or bend radiuses along their run, and the implementation of a safety valve demands perfect adjustment of the valve body to the pipe, the inserting of safety valves into extant pipelines requires intervention at the exact point of insertion, this intervention involving an excavation giving access to the chosen point on the pipeline, a shutting off of the fluid supply downstream, and a local adaptation of the pipeline to the valve, at the insertion point.
Thus, although it is known to insert into a pipeline under pressure, notably for detection purposes, devices of limited size via a point of access-without having to carry out major work on the pipeline, this technique, similar to catheterism for medical exploration, is to date very difficult to use for the laying of safety valves.
Additionally, a safety valve, is known in European Patent No. EP 1 059 481, which does not comprise a tube and therefore does not belong to the previously described model, but comprises a chamber which expands in the event of an excessive fluid flow rate in the pipeline and allows a jacket on the outside of the chamber to bulge and form a valve.
Although this valve can be inserted into an extant pipeline and therefore meets the previously described requirements, its functioning rests on technical compromises difficult to conciliate with long run work.
The present invention, that falls within this context, therefore aims at proposing a safety device likely to be implemented, without excavation work, into a pipeline by inserting it as near as possible to an attachment plug of this pipeline, and having a reliable behavior without requiring the use of materials whose physical properties would be at the limit of the known technical possibilities.